Apparatus and method for spray drying and cooling



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APPARATUS AND METHOD FOR SPRAY DRYINGAND COOLING April 14, 1953 PatentedApr. 14, 1953 APPARATUS AND METHOD FOR SPRAY DRYING AND COOLING GeraldD. Arnold, Wauwatosa, Wis.

Application July 29, 1943, Serial No. 496,574

15 Claims.

This invention relates to improvements in apparatus and methods forspray-drying and cooling.

It is the primary object of the invention to provide'novel and improvedmeans for spray drying and, particularly, to associate such means withmeans for immediately cooling the dried product. It is my purpose to drythe material in a pneumatic convection current of dry hot gas and toseparate the dried product from the drying gases in the same chamber andthe same vortex in which drying is effected.

It is a further object of the invention to provide a method of dryingand cooling whereby the cooling may be eiiected in a continuouslyrecirculated stream of fluid refrigerant which is recooled in suchcircuit, the dehydration of the product precluding the dust-like productfrom adhering to the cooling coils.

Other objects of the invention will be made apparent to those skilled inthe art upon analysis of the following disclosure.

In the drawings:

Fig. 1 is a view partially in side elevation and partially in verticalsection diagrammatically illustratin a drying and coolin um't embodyingthe invention.

Fig.2 is a view taken in section on line 22 of Fig. 1.

Fig. 3 is a view taken in section on the line 3-3 ofFig. 1.

Fig. 4 is an enlargement detail fragmentarily illustrating this positionof the spray nozzle used in the dehydrating section of the apparatus.

Fig. 5 is an enlarged detail showing in section a portion of coolingcoils used in the cooling section of the apparatus.

Fig. 6 is a fragmentary detail of a modified conveyor arrangementillustrated partly insection and partly in side elevation.

Like parts are designated by the same reference characters throughoutthe several views.

The drying and separating chamber 1 has a volute air inlet at 8 for thedrying gas. Such gas is usually heated before its admission and the pipe8 may therefore be understood to communicate with a heater or furnace(not shown).

As the arc of the inlet 8 approaches the cylindrical upper wall 9 of thedrying chamber, it is also inclined helically downwardly, its downwardpitch being approximately equal in one revolution to its thickness sothat the air current delivered to the chamber 1 will tend to pass in onerevolution beneath the current of gas newly admitted. This minimizeseddies in the chamber.

Below the cylindrical portion 9 of the separating and drying chamber,there is a frustov-conical section II) leading to a delivery section IIwhich has a helically pitched undercut shoulder at l2 which acts like ascrew upon the rotatin solids to advance them axially of the chambertoward its discharge port l4.

The chamber is provided at IS with a discharge sleeve for the gases.This communicates by means of boot [6 with the inlet to a blower casing11. The tangential outlet l8 from the blower is preferably arranged topermit the runner of the blower to rotate in a direction opposite tothat in which the gases and dried material rotate in the vortex formedin the separator I. Assuming the vortex in the drying and separatingchamber to rotate counterclockwise as viewed, in Fig. 2 the dispositionof the tangential outlet [8 will be such that the rotation of gases inthe blower chamber l'l will be clockwise. This construction is preferredfor reasons of sanitation, since thereby all baflles on which materialmight accumulate are omitted. However, it is not essential to theinvention. When this feature is used, it will be understood that thevortex in the cyclone may be in etiher direction as long as the vortexin the fan is opposite.

Surrounding the discharge sleeve 15 for the gases is a wall l9 providingan annular well at 20 for a set of spray apertures 23 opposite therespective nozzles 2|. The pipes 22 leading to the several nozzles maybe connected by a header 24 supplied with the material to be driedthrough pipe 25 from a high pressure pump such as gear pump 26. Suchmaterial is usually preheated and concentrated and strained, but the 1inventor is not concerned with this preliminary treatment. The annularwell at 20 in which the several nozzles are disposed is open at its topto permit the nozzles and their associated header to be lifted as a unitfor cleaning or inspection of the nozzles. It preferably, however, isprovided with a cover 200 tightly fitted about pipes 22 to I preventatmospheric air from reaching thechamber 1 through the well 20- andapertures 23. The nozzles and the respective apertures 23 through whichtheir spray is directed are preferably arranged upon a helical pathcorresponding in pitch to the helical path followed by the current ofgases admitted through the conduit,

The.

8 to the drying and separating chamber. stream of drying gas is heldcentrifugally to the cylindrical wall portion 9 of the chamber 1 in thepath or the spray discharged from the several nozzles 2! so that none ofthe atomized mapelled from the separator while the gas, turning.

at this point to escape through outlet sleeve !5, will be substantiallyfree of the dried material.

To minimize the velocity of the air at the point where it leaves theseparating chamber, thereby minimizing the amount of dried product"which Will be carried out of the chamber with the air, I employ theprinciple of rotating the gases in the fan casing in a direction whichis reverseto their direction of rotation in the separating chamber,as-above explained. I have found that the clockwisevortex in thefan'chamber will'be com municated downwardly from the fancasing inlet'until-it interactswith the counterclockwise vortex in the separatingchamber. At this point of interaction, which willusually occurimmediately below the flared inlet 2 to: the discharge sleeve. l5, therotative= velocityof the gases will be: substantially eliminated and.the gases will have'.only avertical or axial velocity which willnot-normally be enough to' liftdust' from the separator.

However, .inasmuch as spray-dried material is frequently of considerablevalue, I preferto em ploya. second stage; of; separation .forremovingfrom. the drying gases the last: vestige of' dust;

The separator 30 in which the second stage separation occurs receivestangentially the discharge from blowerv I'l. It .has av discharge.sleeve. at 31 which'may open at 32 toouterair. Around the sleeve:3lis..a .sleeve33 whichmayrecirculate. some of the .gases. and. dust inthemanner disclosedin my: Patent Ser. No. 466,576, filed November. 23,1942,,now abandoned .entitled Gene triiugal Separators.

Thesolidsare: delivered through discharge end 34 of the secondaryseparatorin: the manner already described and, through pip 35, theyreach'a conveyor. tube 36. intowhich theiirst separator also discharges.

A screw conveyor comprising threesectionsjil,

38 and 39 operates inttube 36. Thesectionsare,

continuous, each with the other, save where interrupted by transversebafiles 40 and 41 which close approximately the upper half of theconveyor tube 36'between the respective conveyor sections. When thematerial dehydrated is being supplied from the separators in sufiicientquantity to substantially fill the tube 36, such material will be passedvirtually without interruption from one conveyor section to another.However, when the material is inadequate to fill the tube, then the gapbetween conveyor sections will tend to allow a.-certain.residuum ofmaterial to remain between .sections where it willcooperate with thebafile. to form aseal precluding any transferof air or. othergas fromone section to the other.

The purpose of this arrangement is to insure.

thesealingofthe conveyor tube to. preclude the mixing. of .the .hot,humid air used for dehydration vwiththe chilled, gas later. used forcooling thematerial- Al1.of the material, whether derived from thedehydrator-separator. 'l or. the secondary separator- 30, passesthroughtheconveyor tube 36 into pipe 43 which is in a closed refrigerationcircuit which includes cooler separator 45, fan casing 46, andrefrigerator casing 41. The cooler separator 45 is preferablysubstantially identical with the separator shown at 3B. The cooling gasset in motion in the fan casing 46 circulates through the closed systemwith sufficient velocity to entrain the material delivered into pipe 43and to project such material tangentially into cooler separator 45 withsufficient velocity for the centrifugal separation of the solids fromthe gas. The solids are discharged through the rotary valve at into abarrel or other container 49. while the gases pass upwardly through thegas return pipe 50 to the eye of th fan casing 46. Since the gasesrotate counterclockwise in cooler separator; the fan casing 46 ispreferably arranged for clockwise circulation so that thevortexcommunicated downwardly from the fan into the separator willoppose and tend to neutralize at some. point within: the'sseparator thevortex established therein,- thus minimizingthe amount of material whichwill be carrie'd'upewardly from'cooler separator "45* with the gases.

However, this is relatively immaterialain the cooling section ofthedevice for: the reason .that': the closed circuit for. refrigeratinggases: pres-- cludesany 'lossof material provided the material 1 hasbeen dehydrated sufficiently andxprovided. further that;theico'oling-coils55 inztheechame" ber' 41 have sufiicienttareaiandoperate .atlsuchl temperatures as not. to; coolth'e refrigerating.

gasesibelow the .dew point;

Under such: conditions thedust like. material.

carriedv with the circulating gases :fromtheicooleri separator'45 andpassing through-the fan-case:

ing 46 will not adhere to the 700113155 butwill. pass through such coilswithgthelgaseous current. and be returned to the separator andcommingled.

with the material newly arriving; through conveyor tube 36.-

The coils themselveswill preferably be designed 1 in such a way as tominimize any, tendency?- for adherence of dust thereto; The refrigerantsupplied from compressor 56 through radiator; 51 preferablypasses'through pipes58 (Fig.5) which are arranged in banks or tiers, theseveral .runs

of pipe. in each tier being, enclosed in ;a common envelope 60 which hassmooth wall surfaces joined above'and below-the tier of ,pipesto'formsmooth walled passages at 6| through which the-- gaseous coolant and anyentrained. dust will pass virtually unimpeded. Thesheaths- 60 .not only1 serve to protect the.pipesthemselves-from. dust.

accumulation, but they also provide 1 extended heat absorption surfacesfor-the coils.

If desired, banks of fin coils may besubstituted as disclosed inmycompanion application entitled Closed Hammer Mill Circuits, executed ofeven date herewith and now Patent No. 2,400,382.

If, notwithstanding, thetendency of the circus-- latinggas to scour thesurfaces 60, shouldany dust accumulate thereon, these surfaces mayreadily be cleaned bymerely opening the,door 62- withwhich thecoolingchamber 4'! is provided; Dehydration of the material acted uponinthe apparatus should preferably becarried to such an extent as toreduce themoisture content of.

thematerial below 10%, and preferably as lowas 6%, to avoid raising thehumidity of .the cool-s ing gas circulating inthe cooling section ofthe: The gas circulated for cooling.

apparatus. purposes should not. becooled below- 32 to. 38

degrees.F., and should .becirculated in suflicient 5.. quantity so thatthe return gas reaching the cooling chamber 41 from the fan shouldpreferably be about 60 degrees. Cooling below 60 degrees F. is not onlyexpensive but tends to cause condensation on the material, undesirablydampening it. Under these conditions the dehydration of the material tothe specified moisture content will keep both the material and thedehydrating gas dry even while passing over the refrigerating coils.

Although it is necessary to discharge to the atmosphere the hot humidair used for dehydration, the auxiliary separator of the type disclosedwill preclude any substantial loss of the dehydrated material at thispoint and the operation of the system in accordance with the methodabove described will prevent the loss of any material whatever in thecooling section. The organization disclosed has the further advantagethat it is not only eflicient and economical of material, but it iscompact and relatively inexpensive and delivers a high quality ofmaterial which would be impossible to achieve but for the immediatecooling following dehydration.

Particularly where the material is a food product it is desirable forthe purpose of promoting sanitation, as well as preventing possible fireloss, to incorporate in each of the several separators an obliquelydisposed partition or wall such as that shown at 65 in thedehydrator-separator i in Fig. 1. This oblique wall 65 spans the anglebetween the wall I9 and the top 9 of the dehydrator separator to excludethe material from what would otherwise constitute dead space in whichdust collects and cakes in the ordinary separator. The wall 85 shouldextend far enough to be secured by the current of newly admitted gasesto prevent any accumulations thereon.

For many installations it may be desirable for the dryer cyclone l andthe auxiliary cyclone 38 to discharge directly into the return conveyorcircuit which handles the refrigerating gases. Fig. 6 suggests apossible arrangement of this sort.

The lower end it of cyclone 1 and the pipe 35 from the bottom of cyclone30, are both shown in Fig. 6 provided with rotary valves 68, 69,operated at a rate to pass all solids but no substantial amount ofdehydrating gases. These valves discharge directly into conduit 430which leads from the cooling chamber 41 to the cooler separator cyclone45. Thus the screw conveyor is dispensed with and pneumatic convectionis substituted, while the humid gases from separators I and 30 are stillexcluded from the refrigerating gas of the closed circuit which includescooler separator 45.

While my apparatus and method have been described in detail it may beappropriate to note by way of summary that the drying of the material tothe predetermined point mentioned permits the cooling thereof in aclosed circuit so that in the entire apparatus there is only one pointat which powdered material can possibly escape, that being in the courseof the necessary discharge of the saturated drying gases. Both thedrying section and the cooling section accomplish a plurality offunctions in the respective vortices. In a single vortex in the chamber1 the material to be dehydrated is dried by the gaseous current in whichit is pneumatically conveyed and is concurrently separated centrifugallyfrom such current. In the vortex of the cooling section the material isnot only cooled by. the. gaseous current by which itis 6. conveyed, butis simultaneously oentrifugally separated from the. gas of such current-In the drying section dehydration is facilitated by the fact that theblower fan used to establish the vortex maintains the chamber 1 undersubatmospheric pressure which reaches a mini-v mum in the centralportion of the vortex into which the material to be dehydrated isreleased by the atomizing nozzles 2|. Under such subatmosphericconditions as exist in the central,- portion of the vortex and in achamber maintained under subatmospheric pressure by the exhaust fan,dehydration of the atomized material is normally instantaneous.

If, in dealing with certain material, it is de-- sirable to provide astream of air about the atomizing nozzle to partially relieve the vacuumor to entrain the atomized product, it is only necessary to omit orremove or open the cover 200 for well '20, whereupon air will beadmitted through the well to enter the chamber 1 through the apertures23, along with the atomized spray.

I claim:

l. A dehydrator-separator comprising the combination with a chamber wallof circular cross section provided with a tangential inlet fordehydrating gas, of a gas discharge sleeve centrally located in saidchamber and about which a current of dehydrating gas flows in a vortex,means for establishing a pressure differential to induce the creation ofa vortex of dehydrating gas, an atomizing nozzle for material to bedehydrated. said nozzle being positioned outwardly radially of saidsleeve and directed outwardly toward said chamber wall for deliveringatomized material into the vortex of dehydrating gas, said tangentialinlet being of substantial radial extent to deliver a moving column ofdehydrating gas across the nozzle in a direction transverse to the axisof the vortex, means disposed outside said sleeve for supplying suchmaterial to said nozzle under pressure to be atomized by the nozzle, andmechanical means for effecting and controlling the discharge ofdehydrated material from the bottom of the chamber, the vortex currentof dehydrating gas in said chamber being adapted to effect both thedehydration of the atomized material and the separation of thedehydrated product centrifugally from the current.

2. A drying and separating chamber including a casing of generallycircular form having a and provided with an outlet for solids, saidcasing being provided with a tangential inlet and a centrally disposedoutlet sleeve for gases, a wall spaced outside of said sleeve andconnected thereto within the casing and forming an annular well betweenthe sleeve and wall, an atomizing nozzle disposed in said well andprovided with supply connections for material to be der hydrated, saidnozzle being directed outwardly toward said casing into the path of gasadmitted thereto from said inlet, and the wall having an aperture forpassing the atomized material from the nozzle to the interior of thecasing.

3. A device of the character described comprising a drying andseparating chamber including a casing with a tangential inlet and acentrally disposed gas outlet sleeve, a wall about said sleeve in spacedrelation thereto, the annular space between the wall and sleeveconstituting a well, means providing a connection between the wall andsleeve within the casing at the bottom of the well, the wall beingprovided with. u

aesagsoa:

spaced. apertures; affording-1* communication bestween the well iandithecasing, a set :of atomizing nozzles within:.the.;well registering withthe respective I apertures for discharging: a spray of atomized materialthrough the: apertures into thezcasing; a header: provided withconnections to theseveral' nozzles for; supplying material thereto; saidheader and nozzles (being unitarilyt movable axially- With respecttmthecasing for withdrawing the nozzles-from the well.

'4.- A drying and separating chamber comprisin combination; achambercasing provided with a tangential inlet and a centrally disposedoutlet sleeve, a fan and fancasing having an inletcommunicatingwith'said sleeve for withdrawing air from-saidcasing anddrawing air intothetangential"lnletof said casing to establisha vortexcurrent therein, a; wall about the sleeveand connectedthereto within thecasing; saidwall being spaced from the sleeve to constitute-therewith anannular" well about the sleeve; and an atomizing 'nozzle disposeclinsaid well and adapted to be withdrawn upwardly therefrom, said-nozzlebeing directed outwardly ofsaid wall into the-path of the'vortex currentof dehydrating gasin-thecasing, and the wall hav-- ingan apertureregistering with the nozzle for admitting the spray of' the nozzleto thesaid current; a

Thedevice of c-laim- 4 in which the inlet of the fan--casing 'is=axially aligned-with the sleeve andthe-blowerfancasing "has a tangentialoutlet providing for vortex rotationin said fan casing in'adirecti'on'opposite to the direction of vortex rotation-in *th'eseparator casing.

1 65' The-deviceof -claim 4 in which the chamber casing is providedabout' said sleeve and Wall with an' obliquelydisposed' false wallextending to the top' of'thecasing and constituting meansfor-excluding-dust from the 'top inner portion of thecasing-closest tothe gas-outlet sleeve;

72 A-drying'and separating chamber compri's-- ing'the combination with achamber casing havinga tangential inlet and a central'outlet casingwithin-the'chamberand an end wallclosing' said and outlets; of means forpassing dehydrating gas and entrained 'material from the-outlet ofone=ofsaid'separators to'the inlet of the other,

each-of 'said'separators having a discharge outletfor solids; and aconveyor system includinga conduit communicating with the aforesaidoutlets for solids-of the respective separators'for receiving-'materialfrom both separators, said conveyorcomprising'aplurality of separatescrew sections-in said conduit; and said conduit having-5 partitionmeans extending transversely of its upper portion between conveyorsections whereby to establish a seal in'said conduit, saidpartitionmeansterminating in spacedrelation to thelower portion of theconduit wherebyto leave a-passage for: solids.

95 Drying" and' cooling apparatus comprising acentrifugaldehydrator-separator provided with a=-tangential-gas inlet, a centralgas outlet and gas-circulating means-for establishing gas flow mtothe:inlet.:and' LOllt" or the outlet forrinducingza vortexaoff dehydrating:gas within the" dehydrator-vseparator between the inlet and outlet, anozzle arranged to discharge material for de hydration into the .vortexwithin the dehydratorseparator, said dehydrator separator having a,

discharge port *for material dehydrated and separated'lin the vortex, arefrigerating separator having'a closed. recirculating gaseous circuitexclusive of said dehydrator-separatoraandinclud+ ing a circulatingblower, means for delivering the" separated dehydrated material fromsaid discharge port into said closed recirculating gaseous circuit whilesubstantially precluding communication of the recirculating gas in theclosed circuit with the dehydrating gas, andmeans for chilling thedehydrated material. in'-- eluding a" refrigerator exposed in saidclosed circult to gas circulated therein by said blower; aconnectionfrom thedehydrator-separator material-discharge part into saidrecirculating gaseous circuitfordelivering-into the closed cir cuit ofthe refrigerating separator solids received from the discharge port of Ythe dehydrator-separator for the cooling of said solids in gascirculating in the closed circuit of the'refrigerating separator and thecentrifugal discharge of the cool solids from such last mentioned gas inthe refrigerating separator, and means controlling thedischarge ofsolids from" the refrigerating separator;

'10. In a dehydrator the-combination with apair of'cycloneseparators'having gas inlets and outlets and means for'passingdehydrating gas and" entrained material from the outlet of one of saidseparators to the inlet of the other, each of said separators having adischarge outlet for solids, ancl a closed conveyor system exclusiveof'said separators and including a tube communicating with theaforesaidsolids outlets of the respective separators for receivingmaterial from both separators, said system comprising a closed pneumaticconveyor meansincorporating said conveyor tube and the respectiveseparator" solids outlets but'isolatedfrom the means for conveying& gasand entrained material betweenseparators, and rotary'means for passingsolids to said tube, while excluding gases from passing from-theseparatorsto the conveyor means.-

11. A method of' dehydration which includes theestablishment of a vortexof dehydrating gas and the spraying of atomized material from within thevortex" outwardly into the vortexto be conveyed and dehydrated by thegas of thevor= tex andiseparated centrifugally from the vortex": by theenergy thereof, the segregation of thedehydrating gas from the solidsseparated there-- from while changing the direction of rotation of thesegregatedgas and the substantiallycontinuous discharge of'both the: gasand the separated solids from the vortex.

12'. The method of dehydration recited in claim 10 in combination withthe further method steps, of delivering such solids substantially freeof dehydrating gas into a closed circuit of circulating cooling gas,establishing a recirculating flow of cooling gas in the closed circuit,establishing a vortex of cooling gas in the closed circuit, and

entraining the dehydrated solids in the cooling; gas of said vortex tobe'simultaneously cooled thereby and centrifugally expelled from saidyor tex, and finally withdrawing the'expelled cooled anddehydratedsolids'from the last-mentioned vortex.

13; The-"method of cooling which involves; the:

establishment of a current of cooling gas in a closed circuit,establishing a vortex of cooling gas in said closed circuit, deliveringfinely divided dehydrated material into said cooling gas to be entrainedthereby for movement with said gas through said vortex and the dischargeof such material independently of the gas from the vortex, substantiallyall of the cooling of the material, as well as its separation from thegas, being efiected in said vortex.

14. In a combination dehydrator-separator and cooler, in which thematerial to be dehydrated is introduced into a vortex of dehydrating gaswherein it is simultaneously dehydrated and separated from such gas, thecombination with closed circuit connections and a cooling gas therein ofmeans for introducing the resulting dehydrated solid directly into thepath of said cooling gas to be entrained thereby, a circulating blowerfor establishing a high velocity current of said cooling gas throughsuch connections, a refrigerator in the path of the circulating coolinggas for abstracting heat therefrom in the course of its circulation, anda centrifugal separating chamber included in said connections and havinga tangential inlet and an axial outlet for said cooling gas and aseparate axial outlet for removing the dehydrated cooled solid, saidblower maintaining a sufiicient velocity of said cooling gas to efiectseparation of the cooled solid from said cooling gas centrifugally inthe said chamber while such solid is being cooled by exposure to therefrigerated gas, said separating chamber having means controlling thedischarge of solids therefrom independently of said cooling gas in saidclosed circuit.

15. In a method of dehydrating and cooling, in which dehydration iseffected in a gaseous vortex at suflicient velocity to separate thedehydrated material from the dehydrating gas, the steps which compriseestablishing cooling gas fiow in a closed circuit in a current withsufiicient velocity to entrain the dehydrated solids, in-

10 troducing said dehydrated solids into said circuit independently ofsaid dehydrating gas to be entrained in the cooling gas current in suchcircuit, establishing in said circuit a vortex of said cooling gas andentrained solids in which the solids are simultaneously cooled andcentrifugally discharged from said current, separating the cooling gasfrom the solids, refrigerating the cooling gas, whereby to extract fromthe cooling gas heat derived from the solids previously cooled, andexpelling the cooled and dehydrated solids substantially free of therecirculating gas, the recirculating gas being confined in said closedcircuit out of contact with said dehydrating gas whereby to avoidcondensation of moisture in the latter.

GERALD D. ARNOLD.

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